What happened
On January 14, 2016, a Boeing 737-400 was performing an approach to landing at Poznań Airport (EPPO). During the landing sequence, after the crew moved the landing gear lever to the DOWN position, they observed that the left main landing gear failed to show a down-and-locked indication.
In response to the lack of indication, the captain instructed the first officer to cycle the gear by moving the lever to the UP position and then back to the DOWN position. After three unsuccessful attempts, a fourth cycle successfully deployed and locked the left main gear, providing the correct cockpit indication. Following the landing and taxiing to the parking stand, the captain reported the incident to the Maintenance Control Center (MCC) and recorded the event in the aircraft technical logs.
The investigation
Technical personnel conducted an inspection of the landing gear system to investigate the cause of the failure. Initial testing focused on a potential malfunction of the down-position sensor, but the system passed the initial tests. Maintenance crews then proceeded to replace the logic card (control module), after which subsequent system tests also yielded successful results.
However, further detailed inspections of the landing gear mechanism revealed that the left main gear extension actuator was not functioning correctly. On January 20, 2016, the left main gear extension actuator was replaced. Following this component replacement, the aircraft was cleared for return to service, and no further issues were reported in subsequent operations.